Sintered carbide hard alloy



United States Patent D 5456 Int. Cl. 'C22c 29/00, 39/28; B22f 7/04 US.Cl. 29-1823 1 Claim ABSTRACT OF THE DISCLOSURE Sintered carbide hardalloys are known in which titanium carbide is embedded in a matrixconsisting of an austenitic steel or a steel hardenable by phasetransformation and/or by precipitation, the alloy being machinable whenthe steel matrix is an austenitic steel or is in a relatively softstate. Such carbide hard alloys however suffer from the defect that theyoften have insufficient abrasionresistance in service, and particularlythat if they are sintered in a very high vacuum they generate a poroussurface layer, and it is difiicult to sinter workpieces right through tothe core.

It has now been discovered that these disadvantages are obviated if thesaid steel matrix is alloyed with from 1.2% to 15% of manganese.

This invention relates to a sintered carbide hard alloy containing 25 to75% titanium carbide and 25 to 75 of a steel which is an austeniticsteel, or a steel hardenable by phase transformation and/or byprecipitation of inter-metallic phases.

Carbide hard alloys produced by powder metallurgy methods havepreviously been proposed which contain up to 75 carbide finelydistributed in a steel matrix as a binder. Such carbide hard alloysdiffer from conventional hard metals in which the binder consisting ofiron, cobalt or nickel, is hardenable. This composition allows thesintered semi-finished products to be machined to their final dimensionsbefore they are hardened, and subsequent hardening being effected by asuitable heat treatment. The advantage of good machinability of thesemifinished product can thus be combined with considerable hardness,which may be as high as 75 RC. Since an alloy containing between 25 and75 carbide cannot be produced by fusion metallurgical methods, thecarbide hard alloy is produced by well known powder metallurgy methods.

Carbide hard alloys usually contain titanium carbide as the carbidecomponent, of which a certain proportion may be replaced by anothercarbide. The binders principally used are austenitic steels or steelswhich are transformation and/or precipitation hardenable. The austeniticand possibly also martensitic steels combine the advantage ofhardenability with the useful properties of being corrosionand hightemperature-resistant. Consequently carbide hard alloys containing thistype of steel matrix can be used with advantage for components that arerequired to possess a satisfactory degree of corrosion resistancetogether with wear resistance and high temperature stability.

In the production of conventional carbide hard alloys difficulties havebeen found to arise when the alloys are sintered in a vacuum lower than10* torr, due to the creation of porous surface layers due tovaporisation. The sinter bodies also tend to be carburised byhydrocarbons and carbon monoxide contained in the furnace atmosphere.Since the generation of a high vacuum exceeding 10- torr increases thecost of production, numerous at- 3,450,51 l Patented June 17, 1969tempts have been made to achieve satisfactory results using a lowervacuum. Thus it has been proposed to avoid vaporisation in the surfacezones and the consequental surface porosity, by binding the titaniumcarbide with chromium carbide to form a substantially saturated mixedcarbide. Although this procedure allows carbide hard alloys to besintered in a lower vacuum, for instance in an ordinary technicalvacuum, and the formation of porous surface zones due to vaporisation tobe suppressed, for unexplained reasons pressings exceeding about 60 mm.in diameter are found not to sinter through to their cores.

Conventional sintered steel-bound carbide hard alloys are usedprincipally as materials for making hotand cold-working tools, which areexposed to a high degree of wear during service. Hardness however is notthe only property required of a material that is to be used for makingwear-resistant components. The decision property of a wear-resistantmaterial is its resistance to abrasion.

Carbide hard alloys hitherto known possess insuflicient resistance toabrasion by foreign pulverulent or granular substances, such as metalpowders, porcelain compositrons, cement, sand and the like, and theinvention provides carbide hard alloys which possess a satisfactoryreslstance to abrasive wear by pulverulent or granular substances.

It has now been found according to the invention that for a sinteredcarbide hard alloy of the type comprising 25 to titanium carbide and 25to 75% of a steel that is an austenitic steel or a steel that ishardenable by phase transformation and/or precipitation of intermetallicphases, the aforesaid properties are provided if the said steel containstogether with other alloying elements, from 1.2 to 15% of manganese.

Although carbide hard alloys of the said type are known which togetherwith titanium carbide in the specified proportions also contain anaustenitic steel matrix or a transformation and/ or precipitationhardenable steel, and which also contain in addition to the said steels,manganese in the stated proportions, it is surprising that when alloyedwith manganese provides a steel matrix which inhibits the abrasive wearthereof by pulverulent or granular foreign substances experienced forinstance by pressing dies for all types of powdered or granular metallicor ceramic products, mixer blades, dressing rollers for grinding wheels,sand blasting nozzles, grinding balls and like components. For example,a carbide hard alloy based on a steel matrix containing no manganese andpossessing a hardness of about 70 \RC has a life when used for profilinggrinding wheels, which despite the relative hardness of the alloy, doesnot exceed that of a steel containing 1.9% manganese and having ahardness of about 63 RC. A carbide hard alloy containing the manganesealloyed in its steel matrix has a comparative life which is five timeslonger.

Furthermore, carbide hard alloys according to the invention possess twoother major advantages which are unexpected and could not have beenperdicted. Firstly sintering of carbide hard alloys according to theinvention can proceed in a vacuum as low as 5.10- torr without theformation of porous surface layers on the sinter bodies due tovaporisation. Secondly pressings having a diameter exceeding 60 mm. canbe sintered through to the core.

The increase in wear resistance of components of a carbide hard alloyaccording to the invention in conjunction with the said two advantagesresult in the carbide hard alloys being greatly superior to that ofconventional carbide hard alloys.

The following examples of the invention are provided.

Example 1 A carbide hard alloy was prepared containing 33% of titaniumcarbide and 67% of a steel consisting of:

The said steel provides a matrix for the carbide hard alloy which ishardenable by transformation and by the precipitation of inter-metallicphases (nickel martensite). The matrix has a hardness in thesolution-treated state of between 45 and 49 RC and after hardening for 6to 8 hours at 480 C., has a hardness between 64 and 66 RC.

Example 2 A carbide hard alloy was prepared containing 33 of titaniumcarbide and 67% of a steel containing:

Percent Carbon 0.90 Vanadium 0.12 Manganese 1.9 Iron Remainder The saidsteel provides a purely martensitic matrix which, having been hardenedby quenching in oil from 810 C. and tempered at 150 to 350 C. accordingto the toughness required, possesses a hardness between 65 and 71 RC,according to temper.

Example 3 A carbide hard alloy was prepared containing 33% of titaniumcarbide and 67% of a steel containing:

Percent Carbon 1.2 Molybdenum 1.5 Manganese 6.0 Iron Remainder The saidsteel provides a martensitic, i.e. transformation-hardenable steel,matrix which still possesses a re sidual austenite content. This alloyachieves its optimum hardness after having been quenched in oil from1040 C. Despite its residual content of austenite the alloy attains ahardness of between 70 and 72 RC.

Example 4 A carbide hard alloy was prepared, containing 30% of titaniumcarbide and 70% of a steel consisting of:

Percent Nickel 3 8 Chromium 1 3 4 Molybdenum 5.75 Titanium 2.75Aluminium 1.60 Niobium 0.70 Boron 0.01 Manganese 1.95 Iron Remainder Thesaid steel provides a steel matrix which is hardenable by theprecipitation of inter-metallic phases. Its hardness when quenched fromin the 'austenitic state was found to be 3 5 to 38 RC, and tempering for16 hours at 790 C. and holding for 16 hours at 650 C., a hardnessbetween 54 and 56 RC was obtained.

Example 5 A carbide hard steel was prepared containing 30% of titaniumcarbide and of a steel containing 1.25% carbon, 12.5% manganese,remainder iron.

The said steel provides a pure austenitic steel matrix due to its highmanganese content, particularly after having been quenched. It is nottherefore magnetic. Thi socalled maganese austenite has substantiallybetter properties with respect to Wear resistance than the nickelaustenite according to Example 4 and that possessed by stainless steels.The hardness of this alloy was measured and found to be 45 to 48 RC.

Carbide hard alloys according to the invention may be produced byconventional powder metallurgical methods. Thus the individualcomponents may be ground to a grain size of about 2 to 5 microns, andthe powder compacted to shapes and sintered. After having been sinteredthe components are machined to their final dimensions and then hardenedby submitting them to a known suitable heat treatment to provide thedesired properties.

What is claimed is:

1. In a sintered carbide hard alloy possessing a high wear-resistance toabrasion and erosion of the type comprising 25 to titanium carbide and25 to 75% of a steel from the group consisting of austenitic,transformation hardenable, precipitation hardenable, and mixturesthereof, wherein the improvement consists in that the steel is alloyedwith from 1.2 to 15% of manganese.

References Cited UNITED STATES PATENTS 2,828,202 3/1958 Goetzel 751233,053,706 9/1962 Gregory 14831 3,183,127 5/1965 Gregory 148-3l 3,369,8912/1968 Tarkan 148-31 3,380,861 4/1968 Frehn 14831 CARL D. QUARFORTH,Primary Examiner. ARTHUR J. STEINER, Assistant Examiner.

US. or. X.R.

